Combustion device with thermoelectrically powered burner



May 25, 1965 w. A. HERBST ETAL. 3,185,201

COMBUSTION DEVICE WITHTHERMOELECTRICALLY POWERED BURNER Filed July 6.1961 2 Sheets-Sheet 1 STY A N ROBERT L. WEEKS JAMES A. WILSON PATENTATTORNEY May 25, 1965 w. A. HERBST ETAL 3,185,201

COMBUSTION DEVICE WITH THERMOELECTRICALLY POWERED BURNER Filed July 6.1961 2 Sheets-Sheet 2 ROBERT L. WEEKS JAMES A WILSON BY @LWB TM PATENTATTORNEY United States Patent O 35,201 COMBUSTEON DEVICE WiTH THERMO-ELECTRICALLY PWERED BURNER Walter A. Herbst, Union, Robert lL. Weeks,Scotch Ilmns,

and James A. Wilson, Stanhope, NJ., assignors to Esso Research andEngineering Company, a corporation of Delaware Filed July 6, 1961, Ser.No. 122,268 4 Claims. (Cl. 15S- 4) This invention relates to a heatingsystem which includes a combustion chamber, a thermoelectric generatorassociated with such chamber, and an electrically activated burner meansincluding a transducer driven by an electronic oscillator powered bysuch generator. This invention relates particularly to an oil burning,home heating system comprising a combustion chamber, a thermoelectricgenerator including a plurality -of thermocouples each having one endintimately associated with such chamber and a hollow burner meansdesigned to admit of passage of a fuel oil stream therethrough,positioned to direct such stream into said combustion chamber.

It has been suggested in the art to associate thermoelectric generatorswith the combustion chamber of a domestic heating plant and utilize theresulting power to activate pumping means associated with the fuelsupply or an air impelling device. In systems of this type the powergenerated must be sufficient not only to transfer the liquid fuel to thecombustion chamber but to provide also through pumping means a sufcientpressure for atomization of such fuel for effective burning. To meetthese power requirements Without a marked increase in thermocoupleproductivity over the present state of that art the size of suchgenerator and the number of producing elements therein can becomeexcessive. In the instant invention highly eiiicient atomization isachieved by ultrasonic vibrational means activated by a low power inputelectronic driver.

In a preferred embodiment of this invention the ow of air or water, pastthe cold ends of the thermocouples, employed to provide the requisitetemperature differential for power generation is effected countercurrentto the temperature gradient in the combustion chamber. This results inmaximum eiciency of heat transfer.

In a preferred embodiment of this invention the heating apparatus isdesigned so as to partition into separate compartments a heat exchangespace provided between an outer housing and an inner combustion chamber,said separate compartments being enclosed by a iirst conduit and asecond conduit formed by said outer housing and the Wall of saidcombustion chamber. One of these compartments provides for circulationof a heat transfer material for space heating, e.g. air or water,another compartment provides a hot water supply within an independentcirculatory system. With the temperature being different for theseparate circulating media this invention is uniquely adapted to and ispreferably carried out utilizing thermoelectric elements which reachtheir maximum eicency at different hot junction temperatures. Inoperation, one junction of a thermocouple is in Contact with a source ofheat while the other is in thermal contact with a heat sink. Thus, thethermoelectric elements herein may be employed in two or more groups andspaced in relation to the temperature gradient along the combustion zonein accordance with their respective eiiiciencies at differenttemperature levels.

A semi-conductor is, as is well known, an electrical conductor with aiinite forbidden energy gap between its valence conduction bands. It iswithin the scope of ll Patented Mey 25, 1h65 this invention to employ asthermoelectric elements semiconductors classified by the art as eitherintrinsic or extrinsic, n-type or p-type. Furthermore, it is within thescope of this invention to employ thermocouples of any composition whichwill perform satisfactorily within the temperatures of operationexisting at the part of the combustion chamber with which such couple isassociated. The size, shape and fabrication of such thermocouples may bevaried so as to adapt to the over-all design of the heating unit.

Among the suitable semi-metallic alloys that may be used forthermoelectric elements are combinations of indium and arsenic; indiumand antimony; lead, selenium and/or tellurium, etc.

Metallic thermocouples, eg. combinations wherein one element is achromium steel alloy and the other is Constantan (a nickel-copper alloy)or Copel, may also be used.

In this invention electrical energy from the thermoelectric generatorassociated with the combustion chamber provides power for an electronicoscillator. The latter serves as a driving means for a transducerapparatus which in turn is utilized to atomize fuel for eiiicientburning. The transducer, when associated with appropriate housing meansand conduit means for receiving fuel, constitutes or is included in theburner device of the instant combination. The transducer employedcomprises a piece of ceramic piezo-electric material such as bariumtitanate bonded to or held in close contact with a at surface to thelarger diametral surface of a stepped cylinder or truncated, conical,etc., resonator of elastic and electrically conductive material such asaluminum.

When an alternating voltage of relatively high frequency is appliedacross the ceramic piece, this piece will be cyclically thickened andthinned and will generate alternate compression and rarefaction waves ofsonic energy. This energy, which may be characterized by a frequencywithin or preferably above the range of normal hearing will cause acyclical lengthening and shortening or longitudinal vibration of themetal resonator as it flows thereinto. With decreasing cross sectionalarea of the resonator in the direction away from the ceramic piece,there will be a concentration of energy near the resonator tip and anincreasing amplitude of motion. When a drop of liquid such as heatingoil is applied to the resonator tip while the resonator is beingvibrated longitudinally, sonic energy will flow into this drop and thedrop will be broken up into a fog of line particles, that is, it will beatomized.

Activation of the transducer so as to perform its intended functionrequires a driving means, that is, a means whereby and wherefromalternating voltage is supplied to the transducer. The driving meansemployed herein comprises an electronic oscillator.

A sonic energy transducer of the kind described is, like many othercomponents used in alternating current circuits, characterized by afigure of merit or efficiency coeiicient generally designated Q Qrepresents the ratio of energy stored in the component to the energylost therein or therefrom during equal intervals of time of an operatingcycle. For a transducer comprising a disc of barium titanate bonded tothe base of a conical aluminum resonator the over-all or composite Qwill often be as great as 2,500. This is a relatively high value, andsignifies that the transducer has quite a sharp resonant peak; that is,its frequency of excitation by input voltages from the driving meansmust lie in a relatively very small range or narrow band for achievementof a substantially maximum amplitude of longitudinal vibration.

The electronic oscillator employed herein is designed to provide Class Coperation with current feedback. The

,are sustained at a selected mechanical harmonic frequency of thetransducer which is dictated by the tuned circuit. Also a safety circuitis included to control the supply of liquid to the transducer in such away that there Will be a flow of liquid only when driving power isfurnished to the transducer.

One object of this invention is to provide a highly eicient home heatingsystem utilizing ul-trasonic vibrational atomization of an oil fuelactivated by a low power input electronic driver and which does notrequire an outside source of electrical power.

Another object of this invention is lto provide an oil fired heatingsystem wherein electrical energy produced therein by thermoelectricgeneration provides power for both fuel atomization and for rechargingduring operation the storage batteries employed for system startup.

Other and further objects of the invention will become apparent as thedescription proceeds, reference being had to the accompanying drawingillustrating one form of the invention wherein:

FIGURE l is a schematic side view in cross section of a fluid fuelburning apparatus having a thermoelectric generator incorporated thereinand equipped with a burner designed to provide fuel atomization viageneration of alternate compression and rarefaction waves of sonicenergy.

FIGURE 2 represents a diagram ofthe electrical circuit suitable for usein effecting the combination of this invention including thethermoelectric generator and sonic energy transducer-burner of FIGURE 1with an electronic oscillator interposed therebetween, such oscillatorbeing powered by such generator and serving as the driving means forsuch transducer.

Referring now to FIGURE l, this is a schematic sideview in cross sectionof a combustion heating apparatus 1 which, in the embodiment shown here,includes a fuel feeder unit 2 and a heater unit 3. Heater unit 3includes an outer housing 8, shown as cylindrical in form, although itcan assume other shapes, enclosing a heating chamber or combustionchamber 9. Around part of chamber 9 is a first heat transfer chamber orcompartment 10 for supplying heat to a space heater circulatory system.A second heat transfer chamber or compartment 11 surrounds a furtherpart of chamber 9 for providing a hot water supply. As it hasV adecreasing temperature gradient from left to right, as seen in FIG. l,the combustion chamber may be considered to have successive temperaturezones or subzones adjacent the respective heat exchange compartments 10and 11. T-hat part of combustion zone or chamber 9 which is adjacentcompartment or chamber 10 may be considered a first zone of hightemperature range. That part which is adjacent compartment or chamber 11may be considered v `a second or lower temperature zone. The outlet ofchamber 9 is an exhaust conduit 12 through which combustion gasesaredischarged from the apparatus. A thermoelectric generator orthermopile 13 is Ybuilt into the wall Y betweenV zone or chamber 9 andthe air or water jacket zone 10 and water jacket zone 11. ThethermoelectricV generator 13 includes a tubular member 14 formed ofelectrically insulating refractory material and which extendscoaxially'with housing 8 so as to define combustionV chamber l9, aplurality of substantially radially extending thermocouples 15 connectedin series or in both series Yandparallel by conductors not shown andhaving hot by tubular member 14whi`ch is a nonconductor.

In one embodiment the thermocouples are protected from direct contactwith the combustion gases of chamber 9 by a combustion chamber liner,not shown. Appropriate material between such liner and thethermoelectric elements provides electrical insulation from the linerwithout appreciably reducing heat transfer. A similar liner, againappropriately insulated, may be disposed between the elements and theheat'transfer chambers 10 and 11. Electrical connection between'theappropriate portions of such elements may be effected by conductors inaccordance withv conventional practice.

Thermocouples 1S in FlGURE l are divided into"high temperaturethermocouples 15a which reach their maxi-Y mum eciency at relativelyhigh temperatures, i.e. within the temperature range existingimmediately -forward of burner 5, hereinafter described, e.g. from about900 to 1700 F., and low temperature thermocouple's. 15b which reachtheir maximum eiiciency at temperatures of up -to about 700 F. belowthose of the aforesaid range. In other words, the high temperaturethermocouples 15a are chosen so that they oper-ate at maximum eihciencywithin the first temperature range or zone and thermocouples 15b arechosen so that they reach Y their maximum efiiciency in the secondtemperature range or zone. YAs is known in the art, the thermoelectricelements are made up of materials known as semi-conductors. A p type andan n type must be in electrical contact to form one junction of thethermocouple. Suicient numbers of the couples `are arranged in seriesand/or parallel arrangements to provide the voltage and amperagenecessary to the operation of the device. The so-called high temperaturetherrnocouples may consist of compositions of iridium and arsenic;compositions of lead, selenium and/ or tellurium which may also includedopings of sulfur, Bi, Ta, Mn, Zn, Ti, Al, Ga, etc. The high temperaturethermocouples and the low temperature thermocouples may consist of thesame materials with a different ratioY of the same components employed.While for purposes of simplification the thermocouples are shown to bedivided into only two groups, it should be understood that more than twotypes of thermocouples, i.e. thermocouples of different design orcomposition, may be utilized in accordance with their eiiiciency ranges.Thus one might employ an iridium-arsenic combination above 900 F.followed by an iridium-antimony combination in the area immediatelydownstream Ifrom the burner where the operating ternperature range isabout 600 to 900 F. and beyond this combinations such as Bi(Te, Se)3.This invention, however, does not reside in the shape or composition ofthe thermocouples employed and it is within the scope of this inventionto use any of the various thermocouple designs and materials known tothe art for thermoelectric generation of electrical energy at operatingtemperatures within the temperature ranges employed in conventional oilburner home heating systems. Conduit 19 provides inlet means for a heattransfer medium, e.g. air or water, to chamber 10 where such mediumacquires heat generated in combustion zone 9 and leaves chamber 10 viaconduit 20 for use in spacerheating.V Conduit 21 provides inlet means tochamber 11 for water to be heated in chamber 11 and passed on to hotwater storage via conduit 22. As indicated by the arrows, theow of heattransfer medium in both chambers is preferably countercurrent to thetemperature gradient, i.e., the cool uid enters the end remote from theburner and exits at the end nearest vthe burner. Wires 24, 25 and 26represent electrical connections for/transfer of electrical energy Yanultrasonic type burner nozzle or Vatomizer 5 having an outlet openingV5a. Fuel oil is admittedjto nozzle 5 by fuel conduit 6 via electricallycontrolled valve 7.. The construction and operation of nozzle 5 andvalve 7 will be discussed in greater detail hereinafter in thedescription of FIGURE 2 andelsewhere in the specification. The outletopening 5a of burner nozzle or atomizer 5 is disposed in substantiallyconcentric alignment with opening 23 into combustion chamber 9. Housing4 is here shown mounted on housing 8 and positioned to circumscribeopening 23 and nozzle 5 which is supported in place by support meanspositioned in the cutaway portion of housing 4, not shown here.Combustion air is admitted to combustion chamber 9 through opening 23around nozzle 5 from an air impelling device, e.g. an electricallydriven fan or blower 41. Fuel oil may be provided to nozzle 5 by eithera gravity feed or pumping means.

Referring now to FIGURE 2 in detail, 13 represents thermoelectricelements mounted so as to be energized by heat generated by burning fuelas portrayed in FIGURE l. They are of different composition so selectedas to provide maximum eliiciency for the temperature range of operation.Conductors 24 and 25 are terminals by means of which the totalelectrical output from all the thermoelectric elements are madeavailable for the operation of the burner operating circuit. Theseelements are connected in series with battery terminals T3 and T4through switches S1 and S2 operated by relay Reon signal from thethermostat on-oif control S3 so that during the Warmup period power forthe operation of the device, power for the transducer or atomizer nozzlecan be provided by storage batteries B1 and B2. (In lieu of batteries,suitable transformers of low frequency A C. house current may be used.)This arrangement has the added advantage that after the device hasreached operating temperature, power from the thermoelectric elementswill be available for recharging the batteries, eliminating the need forrecharging B1 and B2 from time to time by an outside electrical source.On starting up, the thermostat S3 causes S1 and S2 to close. After thethermal generator starts up, the batteries are recharged. A suitablevoltage regulator, not shown, will be provided in the battery circuit toprevent overcharging.

Conductor 26 is a terminal connected to an intermediate point in thethermoelectric element arrangement. Iust suhcient voltage is generatedacross 24 and 26 to provide the necessary power for heating the filamentin a vacuum tube V1, i.e., about 150 milliamperes. A connection is madewith battery B2 through terminals T6 and T4 to provide the necessarylament current during the warmup period. C1A and C1B are 4type M-l50silicon diode rectiiiers. They provide a one-way path for the ow ofelectrical power from the thermal element to the oscillator circuit andbatteries. They prevent the discharge of the batteries when the thermalis less than the battery L1 is a 30-millihenry, 20-ohm DC. inductorwhich affords a low resistance direct current path between the powersupply and the plate of vacuum tube V1. Conversely, it provides a highresistance path for high frequency alternating current, that is, forcurrents having a frequency on the order of 50 kilocycles/sec. andhigher.

Vacuum tube V1 is a type 50L6 beam power tetrode having a SO-voltfilament. C2 is a 0.1 microfarad capacitor which prohibits directvoltage on the plate of vacuum tube V1 from reaching the terminals ofsonic energy transducer or burner nozzle 5. On the other hand, thiscapacitor acts as a coupler affording a low resistance path for the flowof high freqency alternating current to the transducer terminals fromthe plate side of the tube. C3 is a 0.005 microfarad capacitor whichacts as a block to prevent direct current short circuiting to ground ofthe control grid of vacuum tube V1 through grid tuning coil L2, butaffords a low resistance path for the flow of high frequency alternatingcurrent from coil L2 to the control grid.

R1 is a 47-kilohm resistor which provides a path for the iiow of directcurrent induced in the control grid circuit by the presence of highfrequency alternating current at the grid terminal. This resistordevelops a control grid bias for vacuum tube V1. C4 is a 0.1 microfaradcapacitor which isolates the power supply from the frame ground of theequipment, but acts as a coupler to provide a low resistance path forthe ow of high frequency alternating current to the terminals of sonicenergy transducer or nozzle 5. C5 is a 33-micromicrofarad capacitorwhich permits negative feedback from the output circuit to the contro-lgrid of the vacuum tube. Negative feedback from output to input of acircuit generally has the effect of reducing output. It is employed inthe oscillator circuit of this invention to effect an improvement inpower factor, specifically, to improve the phase relation of voltage andcurrent to transducer 5.

L2 is a l0-millihenry grid tuning coil having a Q of at least 100. C6 isa grid tuning capacitor having a range up to 1000 micromicrofarads. Thecombination of inductance and capacitance provided by L2 and C3 is tunedto the mechanical harmonic frequency at which transducer 5 is tooperate, a frequency of 70,000 kilocycles/ sec. for example. L3 is a 0.6microhenry current feedback coil having many times fewer turns than gridtuning coil L2. Coils L2 and L3 are, however, electromagneticallycoupled closely together. The output current from vacuum tube V1 totransducer 5 liows through coil L3, inducing a voltage in coil L2 whichappears at the control grid of the tube. The voltage so appearingrepresents positive feedback, and causes the circuit to sustain itselfin an oscillating condition. This feedback and oscillationsustainingeffect occurs most eciently when grid tuning coil L2 and capacitor C6together are tuned to an active mechanical harmnoic frequency oftransducer 5.

Transducer 5, as shown, comprises a relatively thin disc ofpiezo-electric material P-1 bonded to the larger end of a metallic andelectrically conductive resonator RSwl, shown here, as of truncatedconical form. This transducer, the illustrated design of which isrepresentative only, is characterized by an axial hole 5a through bothelements Pel and RS-l. Fastened to piezo-electric element P-l inalignment with this hole is a liquid feed conduit 6 which includes asolenoid-operated stop valve 7. In the absence of energizing current toits coil element, valve 7 is normally closed.

, C7 is a 10G-microfarad capacitor, and R2 is a lO-kilohm resistor. Highfrequency alternating voltage from vacuum tube V1 appears acrosscapacitor C7 and resistor R2 in series. Capacitor C7 serves to block theow of direct current from the plate of vacuum tube V1. A reasonableamount of high frequency alternating current will be passed by capacitorC7 acting as a coupler between the oscillator circuit itself and thesafety circuit including relay Re-Z which serves to prevent flow ofliquid for atomization to transducer 5 except when the transducer hasdriving power furnished to it.

Resistor R2 acts a a proportioning device in respect of alternatingcurrent passed by capacitor C7 to allow enough current to be supplied torectifier C3 to satisfy the operating requirement of relay Re-Z, aboutZ2 milliamperes direct current, which is normally open across itsexternal terminals T7 and T3. Rectifier C8 is a type IN34 germaniumdevice which receives alternating current from vacuum tube V1, andpasses a pulsating direct current. C9 is a 0.1 microfarad capacitorwhich acts as a storage device for this pulsating current which owsthrough the coil element of relay Re-Z and also through resistor R2.When there is an adequate amount of high frequency alternating currentavailable from the oscillator circuit at capacitor C7, relay Re-2 willbe energized to close across terminals T7 and T3. Upon the effecting ofclosure across these terminals a power circuit will be completed throughthe coil element of solenoid-operated valve 7 to open this valve, andallow liquid for atomization to iiow through conduit 6 into transducer5.

The oscillator as described affords a means of obtaining relativelylarge plate currents at low plate voltages in 7 vacuum tube V1. Thisprovides efficient coupling for transducers such as sonic energytransducer 5 having load resistances in the rangeV of about 100 to 1000ohms. The basic control of oscillation is exerted through thetransducer, and changes in the resonant frequency of the transducer dueto changes in temperature, for example, result in corresdonding changesin the operating frequency of the oscillator.

The resonant frequency of operation of sonic energy transducer 5 is aseries resonant frequency. Accordingly, v

maximum transducer activity or performance is obtained at a condition ofmaximum current. Transducer current flows through feedback coil L3coupled to tuning coil L2 of the grid circuit to provide positivefeedback, and therefore the higher the transducer or output current, thehigher the control grid voltage of tube V1. Grid bias on the vacuum tubeof the oscillator of this invention is sustained at an average levelabout double the amount required to cause plate current to cease toilow.

A -transducer intended to be driven by the oscillator of thisinvention'may have more than one resonant frequency; that is,longitudinal vibrations may be sustained in it at more than onemechanical harmonic or mode designated as half wavelength, fullwavelength, three halves wavelength, etc. It is desirable to select theone of these harmonics for the oscillator/driver operating point whichwill be the most eiiicient with respect to energy conversion in thetransducer. The tuned circuit including coil L2 and capacitor C6 whichis coupled to the output circuit through coil L3 and connected to thecontrol grid of tube Vi is adjusted to provide a relatively broadresonance at the selected mechanical harmonic of the transducer. Suchadjustment results in maximum current feedback at this one harmonic, andoscillator operation is sustained at this point.

' Although this invention has been described with a certain degree ofparticularity, it is to be understood that the present disclosure hasbeen made only by way of example,

8 tion means between the said Wall and housing so arranged, as toprovide partitioned first and second heat exchange compartments, saidcombustion chamber having first and second zones adapted to operate atdifferent temperature ranges, said first heat exchange compartment beingadapted to contain a heat exchange fluid and being located adjacent saidfirst zone, a first series of thermoelectric'couple means operable toproduce maximum electrical output Y within a first temperature rangehaving hot junctions within said rst Zone and cold junctions in saidfirst heat eX- change compartment, said second heat exchange compartmentbeing adapted to contain a heat exchange fluid and beinglocated'adjacent said second zone, a second series of thermoelectriccouple means operable to produce maximum electrical output in a secondand different temperature range having hot junctions Within said secondzone and cold junctions in said second heat transfer compartment, andconnecting means for combining the power outputs of both said series tosupply operating power to UNITED STATES PATENTS 1,599,323 9/26` Frank.2,015,610 9/35 Findley. 2,3 62,25 8 11/44 Findley 126--110 v2,362,25911/44 Fndley 126-110 X 2,453,595 11/48 Rosenthal. 2,481,620 9/ 49Rosenthal Y 158-77 `2,519,241 8/50 Findley a 126-110 X 2,949,900 8/ 60Bodine. v3,121,534 2/64 Wilson 239--102 JAMES W. WESTHAVER, PrimaryExaminer.

FREDERICK L. MATTESON, JR., ROBERT A.V

OLEARY, Examiners.

1. IN APPARATUS OF THE CHARACTER DESCRIBED, THE COMBINATION WHICHCOMPRISES A POWER OPERATED LIQUID FUEL BURNER, HOUSING MEANS ADJACENTSAID BURNER AND ENCLOSING A WALL WHICH DEFINES A COMBUSTION CHAMBER FORSAID BURNER, SAID WALL BEING SPACED FROM SAID HOUSING, PARTITION MEANSBETWEEN THE SAID WALL AND HOUSING SO ARRANGED AS TO PROVIDE PARTITIONEDFIRST AND SECOND HEAT EXCHANGE COMPARTMENTS, SAID COMBUSTION CHAMBERHAVING FIRST AND SECOND ZONES ADAPTED TO OPERATE AT DIFFERENTTEMPERATURE RANGES, SAID FIRST HEAT EXCHANGE COMPARTMENT BEING ADAPTEDTO CONTAIN A HEAT EXCHANGE FLUID AND BEING LOCATED ADJACENT SAID FIRSTZONE, A FIRST SERIES OF THERMOELECTRIC COUPLE MEANS OPERABLE TO PRODUCEMAXIMUM ELECTRICAL OUTPUT WITHIN A FIRST TEMPERATURE RANGE HAVING HOTJUNCTIONS WITHIN SAID FIRST ONE AND COLD JUNCTIONS IN SAID FIRST HEATEXCHANGE COMPARTMENT, SAID SECOND HEAT EXCHANGE COMPARTMENT BEINGADAPTED TO CONTAIN A HEAT EXCHANGE FLUID AND BEING LOCATED ADJACENT SAIDSECOND ZONE, A SECOND SERIES OF THERMOELECTRIC COUPLE MEANS OPERABLE TOPRODUCE MAXIMUM ELECTRICAL OUTPUT IN A SECOND AND DIFFERENT TEMPERATURERANGE HAVING HOT JUNCTIONS WITHIN SAID SECOND ZONE AND COLD JUNCTIONS INSAID SECOND HEAT TRANSFER COMPARTMENT, AND CONNECTING MEANS FORCOMBINING THE POWER OUTPUTS OF BOTH SAID SERIES TO SUPPLY OPERATINGPOWER TO THE BURNER.